This invention relates generally to fuel pumps for combustion engines and more specifically relates to fuel pump assemblies having a vane type pump for supplying fuel to an engine in combination with a dynamic booster pump for delivering fuel from a supply source such as a fuel tank, to the inlet of the vane pump.
Rotary vane type fuel pumps are well known in the aircraft engine art. In the past, design considerations and limitations have required such pumps to include axial shafts having journal ends of relatively small diameter. In this context, the term relatively small refers generally to the diameter of the journal ends of the shaft which are supported by rotary bearings, relative to the central rotor portion of the shaft. For example in vane pumps of known design, if the diameter of the rotor portion was specified as D, it would be necessary, in general, to limit the diameter of the journal end to not more than D-2.times. (depth of the vane slot +0.1). The term journal end refers to the portion of the rotary shaft that is supported by rotary bearings; it will be understood in this regard that such portion of the shaft need not necessarily be located at the extreme end of the shaft.
In co-pending U.S. patent application Ser. No. 08/114,253, filed Aug. 30, 1993, and assigned to the same entity as this application, there is disclosed a new type of variable displacement vane pump in which the diameter of the rotary shaft is made significantly greater than it was in vane pumps of the prior art and which can be substantially uniform in diameter from end to end. Specifically, in the new type of vane pump there disclosed, it is possible for the bearing support portions of the shaft, i.e. the journal ends, to be of substantially the same diameter as the main, vane-supporting portion of the shaft. The present invention relates to this new type of vane pump and the specification of the co-pending application is, accordingly, referred to expressly and incorporated by reference herein.
Limitations inherent in the design of some aircraft, result in the delivery of fuel at relatively low pressure to the inlet of the vane pump or vane pumps that are used as the main source of fuel pressure for the aircraft engines. To meet the requirements for high output pressure to supply the engines, while overcoming the limitations of low inlet pressure coming form the fuel supply reservoir, the practice of using inlet pressure booster pumps has been developed.
In the past, the main engine vane pumps and the booster pumps used to supply the vane pump inlets have been separate and distinct devices. A significant disadvantage of using main engine pumps and booster pumps that are separate and distinct from one another is the resulting substantial increase in "windage" energy losses and the corresponding decrease in pump efficiency. In this regard, "windage" refers to the energy losses incurred when a rotating or other moving surface, such as the surface of the rotary impeller in a booster pump, is constrained to move in close proximity to a stationary surface such as the inner surface of the housing for such a pump. "Windage" losses also include the energy dissipated in the separate sets of rotary bearings used in both the vane pump and the booster pump.
It is desirable, in general, to reduce windage losses so as to increase pump efficiency.
It is desirable, also, to reduce the total space/volume occupied by equipment such as fuel pumps and related components, in the engine area of an aircraft.
Accordingly, it is an object of the present invention to provide a unified engine fuel pump assembly, combining the functions of both a vane pump and a booster pump, to achieve increased energy efficiency.
It is another object of the present invention to provide a unified engine fuel pump assembly having reduced windage losses.
It is still another object of the present invention to provide such a fuel pump assembly having a reduced number of parts.
A further object of this invention is the provision of a unique engine fuel pump assembly having a larger diameter rotary shaft than in prior art vane pumps and a booster pump impeller diameter that is smaller than in prior art devices, and is not substantially larger than the diameter of said rotary shaft, to reduce the overall space/volume requirements of the assembly.
These and other and further objects, features and advantages of this invention will be made apparent to those having skill in this art by reference to the following specification and the accompanying drawings, in which: